A filename extension is a suffix (separated from the base filename by a dot or space) to the name of a computer file applied to indicate the encoding (file format) of its contents or usage. Examples of filename extensions are .png, .jpeg, .exe, .dmg and .txt. Computer-aided is a prefix for several categories of tools (e.g., design, manufacture, engineering) which assist professionals in their respective fields (e.g., machining, architecture, schematics). Computer-aided design (CAD) software assists engineers, architects and other design professionals in project design. Electronic design automation (EDA), or electronic computer-aided design (ECAD), is specific to the field of electrical engineering. Vector graphics use geometric primitives such as points, lines, curves, and polygons to represent images. List of common file formats of data for video games on systems that support filesystems, most commonly PC games. List of the most common filename extensions used when a game’s ROM image or storage medium is copied from an original ROM device to an external memory such as hard disk for back up purposes or for making the game playable with an emulator. In the case of cartridge-based software, if the platform specific extension is not used then filename extensions ‘.rom’ or ‘.bin’ are usually used to clarify that the file contains a copy of a content of a ROM. ROM, disk or tape images usually do not consist of a single file or ROM, rather an entire file or ROM structure contained within a single file on the backup medium. Source.